Automatic wire electrode feeder for wire electric discharge machining devices

ABSTRACT

An automatic wire feeder of a wire electric discharge machine includes an optical sensor for detecting positional information of a wire electrode in an inserting passage between a feed roller for feeding a wire electrode and an upper wire guide; and a control unit for discriminating a state of vibration or deflection of the wire electrode according to the positional information detected by the optical sensor and also for controlling a feeding and rewinding motion of the feed roller according to a quantity of deflection of the wire electrode. Due to the foregoing, buckling caused by an inserting load in the process of automatic wire connection can be positively detected, and the reliability can be enhanced and further the repetition of connecting the wire again can be reduced.

This application is a National Stage Entry Under 35 U.S.C. § 371 ofPCT/JP01/00216, filed Jan. 16, 2001.

TECHNICAL FIELD

The present invention relates to an automatic wire electrode feeder of awire electric discharge machine for machining a workpiece by electricdischarge energy when an electric discharge is generated between thetraveling wire electrode and the workpiece.

BACKGROUND ART

In the case of machining a workpiece by a wire electric dischargemachine, in general, in the initial stage of electric dischargemachining, while a wire electrode, which will be referred to as a wirehereinafter, is being inserted into an initial hole, electric dischargemachining is started, and the wire is cut off at the end of electricdischarge machining, and then the process proceeds to a position atwhich machining of the next profile is started. Accordingly, in order toautomatize electric discharge machining, it is necessary to automatizethe processes of inserting the wire into the initial hole and connectingthe wire, and further it is necessary to automatize the processes ofcutting off and recovering the wire. Therefore, in order to automatizethe above processes, the technique of an automatic wire feeder, in whichthe wire is automatically connected and cut off, has been conventionallyput into practical use.

In this connection, when the wire is automatically connected, an end ofthe wire, which has been cut off, is automatically sent out by a motorand others, and it is necessary for the wire to be inserted into smallportions which are provided in: the inserting passage such as an upperand a lower guide for supporting the wire on the upper and lower sides;an upper and a lower electric contact piece for supplying an electricdischarge machining current to the wire, an initial hole formed in theworkpiece; and a recovery mechanism for recovering the workpiece.Therefore, when the wire is given a heavy frictional load in eachportion described above in the process of automatic wire connection, orwhen the wire is caught by each portion described above, it isimpossible for the wire to be smoothly inserted, and a portion of thewire is buckled up in the wire inserting passage. When the wire isbuckled up in this way and the feeding of the wire is continued, thewire is forced out from the inserting passage at the buckling position,and the feeding of the wire end portion is stopped and the wireconnecting motion is completely stopped.

In order to cope with this situation, Japanese Unexamined PatentPublication No. 01-274926 discloses a technique, which is described asfollows. When it is detected that the wire electrode is not engaged withthe wire recovery device in the process of automatic feeding of thewire, the process is returned to the initial stage. When it is detectedthat the process has been returned to the initial stage, a command tofeed the wire again is given so as to start wire feeding. According tothis technique, when the frictional load is positively heavy or the wireis caught by the inserting passage, it is possible to connect the wireonce more even after a failure of connecting it. However, this techniqueis disadvantageous as follows. Since it takes time for the wire to beengaged with the wire recovery device, the detection time is extended.Further, since the process must be returned to the initial stage eachtime, the entire process time from the detection of failure ofconnecting the wire to the success of connecting the wire is greatlyextended.

Further, when the buckled portion is located at a position lower thanthe cutting mechanism, it is possible to restore the machine to itsoriginal state by cutting and removing this buckled portion. However,when the buckled portion is located at a position higher than thecutting mechanism, it is impossible to remove this buckled portion, thatis, it is difficult to automatically restore the machine to its originalstate. Unless the above problems are solved, operation of the machine iscompletely stopped.

On the other hand, Japanese Unexamined Patent Publication No. 02-160422discloses the following technique. In an upper portion of the wire guidepipe, there is provided a buckling detecting member having a passagemade of conductive material, the diameter of which is large. Also, thereis provided a buckling detecting circuit for detecting a change involtage impressed between the buckling detecting member and the electriccontact piece of the upper guide block. When buckling of the wire isdetected, the wire is rewound to the initial state and the wireconnecting work is repeated. However, in the case where buckling iselectrically detected as described above, the buckled portion must bespecified by the detecting section, which is disadvantageous. Further,in order to increase the sensitivity of detection, it is necessary todecrease clearance between the electric contact section and the wire assmall as possible. When the clearance of the detecting section isdecreased, it becomes difficult for buckling to be caused in thisportion, and buckling is caused in other open portions, which is anincompatible problem.

Further, Japanese Unexamined Patent Publication No. 62-162425 disclosesa technique which will be described as follows. A deviation of the wirefrom a predetermined passage is detected by an optical sensor, and awire draw-back means is operated so as to draw the wire by apredetermined length so that looseness of the wire can be removed, andthe automatic wire connection is started again. However, this techniqueis disadvantageous as follows. In order to positively remove loosenessof the wire, it is necessary to provide a mechanism capable of beingused as a wire draw-back means. Further, when looseness of the wire cannot be completely removed by the above wire draw-back means, it isnecessary to execute the wire winding motion by the feed motor.Therefore, it takes long time to start automatic wire connection again.

Accordingly, in order to prevent buckling of the wire caused in the wireinserting passage in the process of automatic wire connection and inorder to realize a quick automatic wire connection even if the wire isgiven a load in the inserting passage, it is necessary to provide alarge open space in the wire inserting passage and use a sensor, thedetecting sensitivity of which is high, and it is also necessary topositively and quickly conduct a feeding and rewinding motion of thewire by the feed motor. However, when the feeding and the rewindingmotion of the wire are continuously conducted, the wire is vibrated.Accordingly, it is necessary to instantaneously distinguish between astate of deflection of the wire in the wire inserting passage and astate of vibration of the wire, the deflection of which is small.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished to solve the above problems.It is an object of the present invention to positively detect theoccurrence of buckling caused by an inserting load when a wire isautomatically connected. It is another object of the present inventionto reduce the time necessary for reconnecting the wire and enhance thereliability.

An automatic wire feeder of a wire electric discharge machine of thefirst invention comprises: an optical sensor for detecting positionalinformation of a wire electrode in an inserting passage between a feedroller for feeding a wire electrode and an upper wire guide; and acontrol unit for discriminating a state of vibration or deflection ofthe wire electrode according to the positional information detected bythe optical sensor and also for controlling a feeding and rewindingmotion of the feed roller according to a quantity of deflection of thewire electrode.

An automatic wire feeder of a wire electric discharge machine of thesecond invention comprises a control unit, wherein the control unitstops a feeding motion of the feed roller when the quantity ofdeflection of the wire electrode is increased by a predeterminedquantity in the feeding motion of the feed roller, the control unitstarts rewinding after a predetermined period of time, the control unitstops rewinding when the quantity of deflection of the wire electrode isdecreased by a predetermined quantity in the rewinding motion, and thecontrol unit starts feeding the wire electrode after a predeterminedperiod of time.

An automatic wire feeder of a wire electric discharge machine of thethird invention comprises a rate changeover means, wherein the ratechangeover means reduces a feeding rate of the feed roller according tothe number of times of execution of the rewinding motion.

An automatic wire feeder of a wire electric discharge machine of thefourth invention is characterized in that a direction in which thedirectivity of the optical sensor is narrow is made to agree with adirection of the normal line of the surface of the pinch roller andcapstan roller for feeding the wire electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an arrangement view showing the first embodiment of thepresent invention.

FIG. 2 is a schematic illustration for explaining an optical sensor usedfor the invention.

FIG. 3 is a schematic illustration for explaining the principle of anoptical sensor used for the invention.

FIG. 4 is a schematic illustration for explaining the operation of anoptical sensor used for the invention.

FIG. 5 is a flow chart for explaining the operation of an automatic wireelectrode connecting process showing the first embodiment of theinvention.

FIG. 6 is a flow chart for explaining the operation of an automatic wireelectrode connecting process showing the second embodiment of theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1

Referring to FIG. 1, an arrangement of the wire electric dischargemachine of the first embodiment of the present invention will beexplained below.

In FIG. 1, reference numeral 1 is a wire electrode, which will bereferred to as a wire hereinafter, reference numeral 2 is a workpiece,reference numeral 3 is a wire bobbin for supplying the wire 1, referencenumerals 4 and 5 are pulleys for converting a traveling passage of thewire 1, reference numeral 6 is, for example, a torque motor to compose atension control unit, reference numeral 7 is a capstan roller with whichthe torque motor 6 is connected, reference numerals 8 and 9 are pinchrollers, each pinch roller composing a pair with the capstan roller 7,and reference numeral 10 is a tension pulley for giving tension to thewire so as to absorb deflection of the wire 1 in the wire passagebetween the pulley 5 and the pinch roller 8. Reference numeral 11 is anupper wire guide, reference numeral 12 is a lower wire guide, referencenumeral 13 is an upper machining solution nozzle for jetting out amachining solution from an upper portion of the workpiece 2, referencenumeral 14 is a lower machining solution nozzle for jetting out amachining solution from a lower portion of the workpiece 2, referencenumeral 15 is a roller for converting a traveling direction of the wire1 passing through the lower wire guide 12 from a machined portion whenthe workpiece 2 is machined, reference numeral 16 is a guide pipe, andreference numeral 17 is a winding roller for holding and winding thewire 1. In this connection, the torque motor 6, pinch roller 8, capstanroller 7 and pinch roller 9 compose the tension control section 200.

In the wire electric discharge machine composed as described above, thewire 1 is sent out from the wire bobbin 3, and the traveling directionof the wire 1 is changed by the pulleys 4, 5. Then, the wire 1 passesthrough the tension roller 10, tension control section 200, automaticwire feeder body 300 described later, and upper wire guide 11. Afterelectric discharge has been conducted between the wire 1 and theworkpiece 2, the wire 1 passes through the lower wire guide 12, roller15 and guide pipe 16. Then, the wire 1 is wound up by the winding roller17 and recovered into a recovery box not shown. On the other hand, ionexchanging water is supplied to the upper machining solution nozzle 13and the lower machining solution nozzle 14 from a machining solutionsupply device not shown. The thus supplied machining solution is jettedout to a machined portion of the workpiece 2 coaxially with the wire 1.

The pinch rollers 8, 9 composing the tension control section 200 arerollers to press the wire 1 so that the wire 1 can be contacted with thecapstan roller 7 with a sufficiently strong frictional force. The torquemotor 6 controls tension of the wire 1 via the capstan roller 7 so thatan intensity of the tension of the wire 1 can be kept constant when thetorque motor 6 generates a constant intensity of torque in a directionopposite to the feeding direction of the wire 1 in the case of machiningthe workpiece. When a servo motor is used for the torque motor 6 and thefeeding rate is fed back by using a tachometer or a rotary encoder, itpossible to control a rotation of the capstan roller 7 so that thecapstan roller 7 can be rotated at a constant rate in a wire feeding orwire rewinding direction when an automatic wire connection is conducted.

Next, an arrangement of the automatic wire feeder body 300 will beexplained below.

In FIG. 1, reference numeral 20 is a pipe guide to restrict an insertingpassage of the wire 1 in the automatic wire feeder body 300, referencenumeral 21 is a linear cylinder for elevating the pipe guide 20 by airpressure, and reference numeral 22 is a jet nozzle to form a machiningstart hole for starting machining the workpiece 2 from the upper wireguide 11 and to form a water column for restricting an insertion of thewire 1 to the lower wire guide 12.

In the automatic wire feeder body 300, the mechanism is composed asfollows. When an automatic wire connecting motion is started, a forwardend portion of the wire 1, which is located in the cutting electriccontact section 23 described later, is sent out by the capstan roller 7,the rotation of which is controlled at a constant rate. In this case,the capstan roller 7 is rotated clockwise in FIG. 1. At the same time,the pipe guide 20 is lowered, and a forward end portion of the pipeguide 20 reaches a position close to the upper wire guide 11. Theforward end portion of the wire 1 passes in the pipe guide 20 when thecapstan roller 7 is rotated. Then, the forward end portion of the wire 1passes through the upper wire guide 11 and the jet nozzle 22. Afterthat, the forward end portion of the wire 1 passes in the machiningstart hole formed in the workpiece 2 and reaches the lower wire guide12. During this motion, the wire 1 is restricted by the water columnjetted out from the jet nozzle 22. Further, the traveling direction ofthe wire 1 is changed by the roller 15 by an angle of about 90°. Afterthat, the wire 1 passes in the recovery pipe 16 and reaches the windingroller 17. In this way, the automatic wire connection is completed.Reference numeral 100 is a load detecting device, for example, anoptical sensor. This load detecting device 100 detects a state in whichit becomes impossible to conduct an automatic wire connection when thewire electrode 1 can not be smoothly fed because of an obstructioncaused by friction in the inserting passage, a load given to the wire 1by an attached object to the inserting passage and a load given to thewire 1 according to an uneven surface in the machining starting holeformed in the workpiece 2. For example, an optical type proximity sensorcan be used for the load detecting device 100.

In this connection, the automatic wire feeder is provided with anautomatic cutting function in addition to the automatic connectingfunction. According to the automatic cutting function, the wireelectrode 1 is automatically cut off in the case of retrial in which thewire connection is conducted once more from the beginning by cutting offthe wire 1 when the automatic connecting motion has not been completed,and also the wire electrode 1 is automatically cut off in the case ofbreaking of the wire 1 and also in the case of completion of electricdischarge machining. In FIG. 1, reference numeral 23 is an cuttingelectric contact section, reference numeral 24 is a capstan roller usedfor cutting, and reference numeral 25 is a pinch roller. In the case ofretrial motion and also in the case of breaking of the wire, while thewire 1 is being given tension between the capstan roller 7 and thecapstan roller 24 for cutting and also between the capstan roller 7 andthe pinch roller 25 for cutting, an electric current is made to flow ina pair of electric feeder pieces of the cutting electric contact section23. Due to the foregoing, the wire 1 is fused off at a position close tothe cutting electric contact section 23. In the same manner, while thewire 1 is being given tension between the capstan roller 7 and thewinding rollers 17, 18, at the end of electric discharge machining, anelectric current is made to flow between a pair of electric feederpieces of the cutting electric contact section 23. Due to the foregoing,the wire 1 is fused off at a position close to the cutting electriccontact section 23.

Next, referring to FIGS. 1 to 3, operation of the optical sensor 100used in the first embodiment of the present invention will be explainedbelow.

In FIGS. 1 and 2, the optical sensor 100 is arranged at a position wherethe wire 1 is not bound with respect to buckling of the wire 1 causedbetween the capstan roller 7 and the pipe guide 20 when the wire 1 issent out by the capstan roller 7 in the process of automatic wireconnection. Since the mechanism is composed in such a manner that thewire 1 is bound against buckling between the entrance of the pipe guide20 and the winding roller 17, the optical sensor 100 is arranged at theposition where the wire 1 is not bound with respect to buckling causedin the wire 1. In this connection, reference numeral 400 is a controlunit described later.

FIG. 3 is a view showing a positional relation between the opticalsensor 100 and the wire 1, wherein the view is taken from an upperportion. In FIG. 3, reference numeral 101 is a light emitting section,and reference numeral 102 is a light receiving section. Ultraviolet raysemitted from the light emitting section 101 are reflected on a surfaceof the wire 1, and the reflected light is detected by the lightreceiving section 102. Reference numeral 103 is a detecting region. Whenan inserting load is light in the automatic wire connecting process, thewire 1 is located in the detecting region while the wire 1 is being alittle vibrated. However, when an inserting load is heavy in theautomatic wire connecting process, the wire 1 is forced outside of thedetecting region and buckled up. In this case, since the wire 1 is notbound in the tangent direction of the capstan roller 7 and the pinchroller 9, the wire 1 can be somewhat moved. Therefore, it is preferableto use a sensor having a directivity in the tangent and the normal linedirection. This directivity of the sensor is shown by a hatched portionin the view. Due to the foregoing, the detection range can be extendedwith respect to the vibration of the wire 1 in the tangent direction ofthe capstan roller 7 and the pinch roller 9, and it become possible toprevent the occurrence of an over-detection. On the contrary, it becomespossible to enhance the detecting sensitivity by reducing the detectingrange in the normal line direction.

Reference numeral 400 is a control unit. In order to avoid theoccurrence of buckling of the wire 1 in the automatic wire connectingprocess, the control unit 400 controls the torque motor 6 by an outputof the optical sensor 100 so that feeding and rewinding of the wire 1can be controlled.

FIG. 4 is a timing chart of the automatic wire connecting process fordetecting an inserting load and preventing the occurrence of buckling,and FIG. 5 is a flow chart. In FIG. 4, S1 is an output of the opticalsensor 100. When the wire 1 is in the detecting range of the opticalsensor 100, “High” is outputted from the optical sensor 100. When thewire 1 is forced outside of the detecting range of the optical sensor100, “Low” is outputted from the optical sensor 100. Referring to thetiming chart of FIG. 4 and the flow chart of FIG. 5, operation of theautomatic wire connecting process will be explained as follows. S2 is asignal to turn on and off the rotation (normal rotation) of the torquemotor 6 in the feeding direction. S3 is a signal to turn on and off therotation (reverse rotation) of the motor 6 in the rewinding direction.In either signal, “High’ is to turn on, and “Low” is to turn off. AfterS2 is turned on and the wire connection is started (S201, S202), thewire 1 is sent out. When the wire 1 is vibrated and the amplitude of thevibration exceeds a detecting distance of the optical sensor 100, “High”and “Low” of the optical sensor 100 are repeated (S215, S203). Further,when the inserting load is increased and S1 becomes “Low” continuouslyin a period of time not less than a predetermined period of time (T1)(S204), the wire 1 is completely forced out from the detecting range ofthe optical sensor 100. At this time, S2 is turned off (S207) so as tostop feeding the wire 1. At the same time, S3 is turned on (S208) so asto conduct rewinding the wire 1.

Next, when S1 becomes “High” (S209, S210) and the inserting load isreleased and straightness of the wire 1 is substantially recovered, S3is turned off (S211), and after the predetermined period of time T2 haspassed (S212), S2 is turned on again (S206), and the wire 1 starts beingfed. Even after straightness of the wire 1 has been recovered, the wire1 continues vibrating for some time. However, when S2 and S3 are stoppedfor the predetermined period of time T2 at this moment, this vibrationis stopped. Therefore, the probability of wire connection can beenhanced when the wire connection is conducted again.

In this case, in FIG. 5, when S3 in which the wire 1 is reversely fed isturned on, the number of times is counted by the counter P (S205), andthen the number of times of the reverse feeding motions conducted at thesame position by the inserting load can be stored. If the above motionsare repeated by the number of times not less than a predetermined numberof times (S206), the wire 1 is cut off (S214), and the automatic wireconnecting process is started again. Due to the foregoing, in the casewhere the wire 1 is damaged when the normal feeding motion and thereverse feeding motion are repeated, the occurrence of an error ofautomatic wire connection can be prevented. In order to discriminatethat the reversion has been made by the number of times not more than apredetermined number of times at the same position where the insertingload exists, the counter P for counting the number of times may be reset(S216) when wire feeding (normal rotation) is turned on for a period oftime and more (S215).

In FIG. 5, when the motions of the above processes (S201) to (S216) arerepeated, processing of preventing the occurrence of buckling withrespect to the inserting load capable of conducting a wire connectionagain in the case of automatic wire connection can be realized, andfurther the reliability of wire connection can be enhanced. Accordingly,it is possible to decrease the number of times of connecting the wireagain. Therefore, it is possible to reduce the total automatic wireconnecting time.

Embodiment 2

With respect to the inserting load, the slower the normal rotationfeeding rate is reduced, the higher the reliability of automatic wireconnection can be enhanced. Therefore, in the first embodiment shown inFIG. 6, after the normal rotation feeding motion and the reverserotation feeding motion have been repeated by a predetermined number oftimes, a rate of the normal rotation feeding motion may be decreased.This is shown in the second embodiment.

In FIG. 6, explanations of the same motions as those of the firstembodiment are omitted here. When the counted number of times P hasincreased to a value not less than a predetermined number of times(S206), the normal rotation feeding rate is reduced by a predeterminedratio (S217), and the wire 1 is cut off and the automatic wireconnecting process is started again. When the normal rotation feedingmotion has continued for a predetermined period of time with respect tothe inserting load (S215), the counter P is reset (S216), and the normalrotation feeding rate is reset at the initial value (S218). Due to theforegoing, when the inserting load is heavy, the feeding rate of thewire 1 can be decreased, and when the inserting load is light, thefeeding rate of the wire 1 can be increased. Therefore, the reliabilityof automatic wire connection can be enhanced, and a period of timenecessary for automatic wire connection can be reduced.

As explained above, an automatic wire feeder of a wire electricdischarge machine of the first invention comprises: an optical sensorfor detecting positional information of a wire electrode in an insertingpassage between a feed roller for feeding a wire electrode and an upperwire guide; and a control unit for discriminating a state of vibrationor deflection of the wire electrode according to the positionalinformation detected by the optical sensor and also for controlling afeeding and rewinding motion of the feed roller according to a quantityof deflection of the wire electrode. Therefore, the occurrence ofbuckling caused by the inserting load in the process of automatic wireconnection can be positively detected, and the reliability can beenhanced and further the repetition of wire connection can be reduced.

An automatic wire feeder of a wire electric discharge machine of thesecond invention includes a control unit, wherein the control unit stopsa feeding motion of the feed roller when the quantity of deflection ofthe wire electrode is increased by a predetermined quantity in thefeeding motion of the feed roller, the control unit starts rewindingafter a predetermined period of time, the control unit stops rewindingwhen the quantity of deflection of the wire electrode is decreased by apredetermined quantity in the rewinding motion, and the control unitstarts feeding the wire electrode after a predetermined period of time.Therefore, it is possible to enhance the reliability in the case ofconnecting the wire again.

An automatic wire feeder of a wire electric discharge machine of thethird invention comprises a control unit having a rate changeover means,wherein the rate changeover means reduces a feeding rate of the feedroller according to the number of times of execution of the rewindingmotion. Therefore, the reliability of automatic wire connection can beenhanced, and a period of time necessary for automatic wire connectioncan be reduced.

An automatic wire feeder of a wire electric discharge machine of thefourth invention is characterized in that a direction in which thedirectivity of the optical sensor is narrow is made to agree with adirection of the normal line of the surface of the feed roller forfeeding the wire electrode. Accordingly, when a detection range withrespect to the vibration of the wire electrode in the tangent directionis extended, the over-detection can be prevented. On the contrary, whena detection range with respect to the vibration of the wire electrode inthe normal line direction is reduced, the detection sensitivity can beenhanced.

INDUSTRIAL APPLICABILITY

As described above, according to an automatic wire electrode feeder of awire electric discharge machine of the present invention, buckling of awire electrode caused by an inserting load in the process of automaticwire connection can be positively detected and the reliability ofconnecting the wire again can be enhanced.

What is claimed is:
 1. An automatic wire feeder of a wire electricdischarge machine comprising: an optical sensor for detecting positionalinformation of a wire electrode in an inserting passage between a feedroller for feeding a wire electrode and an upper wire guide; and acontrol unit for discriminating a state of vibration or deflection ofthe wire electrode according to the positional information detected bythe optical sensor and also for controlling a feeding and rewindingmotion of the feed roller according to a quantity of deflection of thewire electrode.
 2. An automatic wire feeder of a wire electric dischargemachine according to claim 1, wherein the control unit stops a feedingmotion of the feed roller when the quantity of deflection of the wireelectrode is increased by a predetermined quantity in the feeding motionof the feed roller, the control unit starts rewinding after apredetermined period of time, the control unit stops rewinding when thequantity of deflection of the wire electrode is decreased by apredetermined quantity in the rewinding motion, and the control unitstarts feeding the wire electrode after a predetermined period of time.3. An automatic wire feeder of a wire electric discharge machineaccording to claim 1 or 2, wherein the control unit reduces a feedingrate of the feed roller according to the number of times of execution ofthe rewinding motion.
 4. An automatic wire feeder of a wire electricdischarge machine according to claim 1 or 2, wherein a direction inwhich the directivity of the optical sensor is narrow is made to agreewith a direction of the normal line of the surface of the feed rollerfor feeding the wire electrode.